A comet is about to come very close to Mars, and NASA is ready

A speeding comet the size of a mountain will come within 87,000 miles of Mars on Oct. 19, and NASA is planning to observe it with just about everything the agency's got.

In a press conference Thursday, officials described how they will use more than a dozen NASA assets including three Mars orbiters, two Mars rovers, and a suite of telescopes to see comet C/2013 A1, also known as comet Siding Spring, from several different angles and in different lights.

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"Normally you send spacecraft to comets," said Kelly Fast, a program scientist at NASA. "Here, the comet is coming to our spacecraft."

Comet Siding Spring was first spotted in January 2013, near the end of its million-year journey toward the sun. Scientists estimate that its nucleus is between half a mile and 5 miles wide. The gas cloud that surrounds its head is 12,000 miles across. Its massive tail extends the distance between Earth and the sun.

And it will be going fast. When the comet makes its closest approach to Mars at 11:27 a.m. PDT, it will be hurtling through space at 126,000 miles per hour.

Scientists are eager for any opportunity to study the bodies that zip through our solar neighborhood, but Siding Spring is especially enticing. That's because it gives humanity our first chance to get an up-close look at a comet from the Oort cloud, a collection of icy bodies at the edge of our solar system.

Embedded in the nuclei of Oort cloud comets are primordial materials from the dawn of the solar system that have been in a deep freeze for billions of years, researchers say. But as the comet moves toward the sun, the ices trapped in its nucleus begin to sublimate, releasing ancient gases into space.

"This particular comet has never before entered the inner solar system, so it will provide a fresh source of clues to our solar system's earliest days," said John Grunsfield, associate administrator for NASA's Science Mission Directorate, in a statement.

NASA's various assets in space, on Mars, and here on Earth will be deployed to look at the size and shape of Siding Spring's nucleus, the composition of the gases in the comet's coma, and how much water it is spewing into space. The Curiosity and Opportunity rovers will turn their cameras toward the Martian sky and, fingers crossed, capture the first image of a comet from the surface of another planet. The orbiters will study how the Martian atmosphere responds to the comet's flyby.

The researchers said the first images from the flyby should be released by Oct. 20. There will also be more information coming next week about how to follow along through social media.

Comet's are notoriously unpredictable, so scientists cannot say for sure what will happen when Siding Spring approaches Mars. All of us, even the experts, will have to wait and watch.